Shoe construction

ABSTRACT

An article of footwear having an upper ( 10 ) with a rear portion ( 14 ) flexible enough to allow the rear part of the sole ( 16 ) to lie flat under the heel of the foot during the walking stride, and flexible enough to permit unimpeded hindfoot inversion; a level sole ( 16 ); an insole ( 20 ) with a gripping material ( 18 ) bonded to its upper surface; and a midsole ( 22 ) that provides shock absorption for the heel and forefoot without springiness. Full range of motion of the foot, balance of the foot and body, and proprioceptive and tactile sensitivity of the foot are achieved.

CROSS-REFERENCE TO RELATED APPLICATIONS

[0001] Not Applicable

FEDERALLY SPONSERED RESEARCH

[0002] Not Applicable

SEQUENCE LISTING OR PROGRAM

[0003] Not Applicable

BACKGROUND OF THE INVENTION

[0004] 1. Field of Invention

[0005] This invention relates to shoes, specifically to shoes for general purpose activities, including walking on hard outdoor surfaces. The invention includes an upper that is flexible in the back, a sole that provides shock absorption without springiness, and an insole with a gripping surface.

[0006] 2. Background of the Invention

[0007] A shoe, ideally, should allow the foot to assume the neutral position when it is not bearing weight, and operate through its full range of motion during the walking and running strides. The conventional shoe, illustrated in FIGS. 1a and 1 b, prevents the foot from ever assuming the neutral position, and significantly impedes the foot's freedom of motion during the stride. It does this primarily through the shape of the surface where the shoe meets the foot. The surface, viewed from the side, displays an S-curve whose lines are determined by a raised heel, a downward slope from the front of the heel to the back of the forefoot, and an upward curve from the back of the forefoot to and past the tips of the toes. The S-curve keeps the forefoot in a chronically plantarflexed position, with the toes, particularly the large toe, chronically hyperextended. The result is persistent stress on the structures of the foot.

[0008] One particular problem with the S-curve is the way it impedes the action of the hindfoot in walking. As the heel lifts off the ground in the heel rise period of the gait cycle, the hindfoot makes a motion known as hindfoot inversion, consisting of a medial twist and a rotation (counterclockwise, viewed from the rear in the case of the left foot, clockwise in the case of the right) relative to the forefoot. (The terminology and description of the gait cycle follows that of Michael M. Whittle, Gait Analysis (2 d ed.) (Butterworth-Heinemann, Oxford: 1996.)) Hindfoot inversion continues through the toe-off period. With many, if not most people, the medial longitudinal arch flattens in the early stage of hindfoot inversion: if flattening is blocked, the heel cannot properly rise and the person cannot take a full stride. The S-curve acts as a barrier to this flattening. The effect may be worsened by the presence of arch supports under the medial longitudinal arch. In addition to the effect of the S-curve, the stiff back portion of the upper, typically reinforced by a heel counter, may contribute to the restriction of hindfoot inversion by holding the hindfoot in a vertical attitude. The result of all this is that wearers of shoes are unable to take a full, natural stride: instead, they are forced to alter their gait in in an awkward and stressful way.

[0009] The flattening or downward deflection of the medial longitudinal arch has a shock absorbing function. That function is impeded when the S-curve prevents the arch from flattening.

[0010] The S-curve is found in all, or virtually all shoes sold today for general purpose use, as well as in popular brands of athletic shoes. Women's high-heel shoes feature an exaggerated S-curve. Even the occasional heelless athletic shoe invariably has a toe spring (the upward curve from the back of the forefoot to and past the tip of the toes), resulting in a partial S-curve.

[0011] Another problem with the conventional shoe is that the raised heel causes stress by tilting the body forward when standing. To maintain balance, the body must take compensatory action, including arching of the back and tightening of the leg muscles.

[0012] A further problem with the conventional shoe is that it causes a significant loss of proprioceptive and tactile sensitivity of the foot. Confined to the S-curve, the foot does not feel the ground with as much accuracy as a bare foot. Loss of tactile sensitivity reduces balance during movement, and the loss of sensory feedback has been implicated as a cause of injuries in runners who wear modern running shoes.

[0013] The present invention offers an alternative to the conventional shoe architecture in a shoe suitable for general purpose use. It avoids the problems of the S-curve by having a flat sole. In addition, it provides an optimal degree of shock absorption and internal traction (i.e., between the top of the insole and the bottom of the foot). Shock absorption is calibrated to maintain the proprioceptive and tactile sensitivity that is possible only with a flat shoe. The back of the upper is kept flexible to facilitate hindfoot inversion and to make the shock absorption features work effectively.

[0014] Prior art has offered some of these features separately, but never together in a shoe suitable for general use.

[0015] A general purpose shoe with flat soles and no heel is disclosed in U.S. Pat. No. 1,117,246 to Roese. The shoe described makes no provision for shock absorption, internal traction, or flexibility in the back of the upper.

[0016] A flat gymnastics shoe designed to preserve tactile sensitivity of the foot is disclosed in U.S. Pat. No. 4,541,186 to Mulvihill. The shoe is specifically designed for gymnastics and similar indoor activities, and lacks the sturdiness and shock absorption necessary for outdoor use. Its slipper-like appearance would not be suitable for a general purpose shoe.

[0017] A heelless sports shoe is disclosed in U.S. Pat. No. 3,555,697 to Dassler. The shoe is specifically designed for use on tracks covered with a layer of resilient material. Accordingly, it has no means for shock absorption, making it unsuitable for general use.

[0018] A shoe with a level sole is disclosed in U.S. Pat. No. 6,021,588 to Alviso. The issues of traction and proprioceptive and tactile sensitivity are not discussed. The drawings show heel counters and heel cups that would reduce tactile sensitivity.

[0019] A shoe with high friction in the front portion of the insole is disclosed in U.S. Pat. No. 5,586,398 to Carlson. The shoe is not flat from front to back, but has a type of negative heel. It also has a “toe ledge” that would chronically hyperextend the toes. One of the diagrams explicitly shows a heel cup (including a heel counter) and others appear to show a reinforced back of the upper.

[0020] An insole whose upper layer is made of a slip resistant material is disclosed by U.S. Pat. No. 5,388,349 to Ogden. The drawings show the insole placed in a conventional shoe.

[0021] Sneakers and basketball shoes, commonly available on the market, often have flat soles. The soles are composed of highly resilient rubber, making them optimal for jumping vertically on hardwood or concrete surfaces, but reducing tactile sensitivity in general use. They do not have high traction insoles, relying instead on a lacing system and cloth upper that allows the front part of the sneaker to be tightly wrapped around the length of the forefoot.

[0022] The Hersey Custom Shoe Company of East Wilton, Me., manufactures athletic shoes with a midsole consisting of shock absorbing ethylene vinyl acetate. At least one model has a sole that is flat from the back to the base of the toes, though it has toe spring from that point forward. The shoes have a heel counter and do not have a high traction insole.

SUMMARY OF THE INVENTION

[0023] The shoe construction of the present invention provides an upper portion connected to a sole portion. The sole portion preferentially consists of interconnected portions, including at least an insole portion, a midsole portion and an outsole portion. The sole portion is of substantially even thickness throughout its length.

[0024] The rear portion of the upper is sufficiently soft and flexible to indent slightly on heel strike and to accommodate the normal inversion of the hindfoot as the heel rises during the gait cycle.

[0025] Preferably, a material of selected coefficient of friction is bonded to the upper surface of the insole in order to provide strong traction between the foot and the shoe.

[0026] In the preferred embodiment, the midsole is composed of a front portion, lying under the forefoot and midfoot, and a rear portion, lying under the heel of the foot, bonded together in a bevel joint. Preferably, the rear portion of the midsole is composed of a material with just enough resilience to provide shock absorption on J heel strike. Preferably, the front portion of the midsole is composed of a material with enough flexibility to bend at a 60° angle at the base of the forefoot.

[0027] Overall, the shoe works like a portable road, carried by the feet. When standing and walking, the wearer experiences a firm ground under his feet, with excellent qualities of firmness, shock absorption and traction, and without coercion or restraint of the actions of the foot and the rest of the body. When sifting, the wearer's feet easily rest in the neutral position. Under all conditions, the feet are free to act as though the wearer were barefoot.

BRIEF DESCRIPTION OF THE DRAWINGS

[0028]FIG. 1a is a lateral elevational view of a conventional men's shoe.

[0029]FIG. 1b is a lateral view of a conventional men's shoe at initial heel strike.

[0030]FIG. 2 is a medial elevational view of the oxford style of the shoe construction.

[0031]FIG. 3 is an a medial elevational view of the insole of the shoe construction.

[0032]FIG. 4 is a medial elevational cross-sectional view of the shoe construction and the left foot in the initial contact period, loading response phase, of the walking gait cycle. (The feet illustrated in FIGS. 4, 5 & 6 are taken from Eadweard Muybridge, The Human Figure in Motion (Dover Publications, New York: 1955) Plate 2, Frame 3; Plate 3, Frames 1 & 5.)

[0033]FIG. 5 is a medial elevational cross-sectional view of the shoe construction and the left foot in the opposite toe-off period, mid-stance phase, of the gait cycle.

[0034]FIG. 6 is a medial elevational cross-sectional view of the shoe construction and the left foot in the toe-off period of the gait cycle.

[0035]FIG. 7 is a rear elevational cross-sectional view of the shoe construction and the left foot in the heel rise period of the gait cycle.

DETAILED DESCRIPTION

[0036] A preferred embodiment of the shoe construction is illustrated in FIGS. 2 and 3. This embodiment is in the form of an oxford style shoe. The shoe construction consists of an upper portion 10 and a sole portion 16. Upper 10 consists of a vamp 12 and two quarters 14. Sole 16 consists of an insole 20, a midsole 22 and an outsole 28. Midsole 22 consists of a front part or portion 24, and a rear part or portion 26. A layer of gripping material 18 is bonded to the upper surface of insole 20. For purposes of this patent, “gripping material” means a material with a selected coefficient of friction (“COF”). The upper and lower limits of COF are set by the action of the toes. The toes reach forward as the forefoot comes down following the intial contact period, curl down and back during heel rise, and dig in during toe-off. COF of the material must be low enough to allow the toes to slide across its surface as they curl back, but high enough to restrain them from sliding during toe-off. A class of items denominated as gripping materials is commercially available for uses such as wrapping the shafts of golf clubs. One such gripping material, sold by 3M Corporation under the name GREPTILE has been found to give satisfactory results in the shoe construction.

[0037] Alternately, the upper surface of insole 20 can be treated to have the characteristics of a gripping material, or insole 20 may be composed of a gripping material.

[0038] Insole 20 is composed of a material sufficiently flexible to bend at a 60° angle as illustrated in FIG. 6.

[0039] Rear midsole 26 is composed of a material of sufficient resilience to provide shock absorption on heel strike, but not so resilient as to give a feeling of springiness. “Springiness” means that the wearer does not feel the hardness of a hard walking surface. Springiness is undesirable for at least 4 reasons: (1) on heel strike, the heel of the foot will make a longer downward excursion into a springy material than a non-springy material and will sink deeper into the material than will the forefoot, thereby excessively stretching the tendons and muscles of the hindfoot and ankle; (2) springiness diminishes proprioceptive and tactile sensitivity; (3) springiness encourages the wearer to pound down on his heels as he walks; (4) if the material acts as an actual spring in the sense of returning energy to the foot in the direction opposite to that of the foot's downward motion, then the heel of the shoe will have a resonant frequency which will tend to impose its own rhythm on the wearer's stride.

[0040] Front midsole 24 is composed of a material of sufficient resilience to provide shock absorption without springiness on forefoot contact, and also to be able to flex at a 60° angle in the toe-off period of the gait cycle, as illustrated in FIG. 6. Since the force of forefoot contact is less than that of heel strike, and the area of contact is wider, it is possible to satisfy these criteria with a material of higher resilience than that used in rear midsole 26.

[0041] Ethylene vinyl acetate (“EVA”) with a Shore A hardness of approximately 45 has been found to give satisfactory results in rear midsole 26, and EVA with a Shore A hardness of approximately 35 has been found to give satisfactory results in front midsole 24.

[0042] Front midsole 24 and rear midsole 26 may be bonded in a bevel joint as illustrated in FIG. 1 but other types of joints are possible. The exact relative lengths of front midsole 24 and rear midsole 26 are not critical, so long as front midsole 24 extends far back enough for the shoe to be able to flex as shown in FIG. 6 (it being assumed that rear midsole 26 is not sufficiently flexible to bend at a 60° angle).

[0043] Outsole 28 must be flexible enough for the shoe to bend as shown in FIG. 6. Aside from that, it may be of any composition and bottom-surface geometry appropriate to the purpose for which the shoe will be used.

[0044]FIG. 4 shows the shoe construction with the left foot in the initial contact period, loading response phase, of the gait cycle. This is just after the heel's initial impact with the ground, as the foot is beginning to plantarflex toward the ground. The portion of sole 16 under the heel of the foot provides shock absorption on a hard surface without springiness. The indentation, or fold, in the back of quarters 14 is made possible by the softness of the material of which they are composed. This folding allows the back portion of sole 16 to lie flat under the heel of the foot. In the conventional shoe, as illustrated in FIG. 1b, the back retains its shape during heel strike and the shoe has to pivot on its back corner in order for the forefoot to come down.

[0045]FIG. 5 is a sectional view of the shoe construction illustrating the position of the left foot in the opposite toe-off period, mid-stance phase, of the gait cycle. The foot is essentially in the neutral position. In contrast to conventional shoes, the heel is not tilted up and the toes are not curled back. The medial longitudinal arch is almost flat.

[0046] When standing in the shoe construction, the foot's position is essentially the same as that of the mid-stance phase of the gait cycle, except that the longitudinal arches are less flattened. The body is better balanced than in the conventional shoe because the shoe construction does not tilt the body forward.

[0047]FIG. 6 shows the shoe construction with the left foot in the toe-off period. The dorsal and plantar surfaces of the foot are bent approximately 90° at the base of the large toe. A line drawn from the base of the large toe to the bottom of the heel of the foot describes approximately a 60° angle to the ground. The shoe has sufficient flexibility to accommodate this much bending. Sole 16 provides a flat surface beneath the toes and ball of the foot.

[0048] Gripping surface 18 of insole 20 comes into play in this stage. The force applied by the forefoot has a substantial rearward component. That rearward component generates a forward ground reaction force, which is what ultimately propels the body forward. The conventional shoe positions part of the S-curve under the front of the midfoot, where the foot can push back against it, thus enlarging and vertically tilting the area where rearward force is applied, somewhat like a starting block. This allows the inside of the shoe to have a relatively low coefficient of friction. In a flat shoe, where the rearward force is all applied on a horizontal surface, the coefficient of friction must be higher.

[0049]FIG. 7 is a rear sectional view of the shoe construction with the left foot in the heel rise period of the gait cycle. The hindfoot is in its initial phase of rising off the ground, while the forefoot is still on the ground. As noted above, hindfoot inversion occurs at this point, continuing as the heel rises into the toe-off period. Because the back of quarter 14 is soft, it does not resist hindfoot inversion.

[0050] Accordingly, the reader will see that the shoe construction of this invention provides the wearer with unique advantages of range of motion, proprioceptive and tactile sensitivity, and balance. These advantages make the invention useful for a range of purposes beyond day-to-day walking and standing. For example:

[0051] The balance, proprioception and tactile sensitivity provided by the shoe construction makes it useful as a therapeutic shoe for people with diminished balance or strength.

[0052] The non-tilting and full range of motion provided by the shoe construction results in less stress at the knees and hips than with conventional shoes, making the shoe useful for people with joint disease or injury.

[0053] The balance, proprioception and tactile sensitivity provided by the shoe construction makes it useful as a golf shoe.

[0054] The grip, balance, proprioception and tactile sensitivity of the shoe construction makes it useful for a wide range of athletic activities.

[0055] Moreover, the principles of the present invention may be embodied in shoe styles other than the oxford style illustrated herein.

[0056] Although the description above contains many specificities, these should not be construed as limiting the scope of the invention but as merely providing illustrations of some of the presently preferred embodiments of this invention. Thus the scope of the invention should be determined by the appended claims and their legal equivalents, rather than by the examples given. 

1. A shoe for use on hard outdoor surfaces comprising an upper portion and a sole portion; said upper portion having, in the portion thereof covering the hindfoot, sufficient flexibility to deform in response to the upward ground reaction force transmitted through the sole in the initial contact period of the walking gait cycle, and sufficient flexibility to deform in response to the motions of the hindfoot during hindfoot inversion; said sole portion being of substantially equal thickness throughout its length and lying substantially flat along its entire length when not subjected to bending forces, and comprising an insole portion, a midsole portion and an outsole portion; said insole portion having sufficient flexibility to bend at an angle of approximately 60° under the forces exerted by the foot from the heel rise to the toe-off periods of the walking gait cycle, and having substantially its entire upper surface a coefficient of friction sufficiently low to allow the toes to slide across it during the heel rise and opposite initial contact periods of the walking gait cycle, and sufficiently high to restrain the toes from sliding across it during the toe-off period; said midsole portion comprising a front portion extending from the front of the shoe to a point between the ball of the foot and the front of the heel, and a rear portion extending from the back of the front portion to the back of the shoe; said front portion being composed of a material with sufficient flexibility to bend at an angle of approximately 60° under the forces exerted by the foot from the heel rise to the toe-off periods of the walking gait cycle, and with a level of resilience such as to provide shock absorption for the forefoot upon forefoot contact without springiness; said rear portion being composed of a material with a level of resilience such as to provide shock absorption for the heel of the foot upon heel strike without springiness; said outsole portion composed of a material with sufficient flexibility to bend at an angle of approximately 60° under the forces exerted by the foot from the heel rise to the toe-off periods of the walking gait cycle, whereby the foot is able to assume the neutral position when not actively flexing, is able to move through its entire range of motion when striding, and is able to experience proprioceptive and tactile sensitivity comparable to an unshod foot.
 2. The shoe for use on hard outdoor surfaces as in claim 1, wherein the upper surface of the insole is treated to have the selected coefficient of friction.
 3. The shoe for use on hard outdoor surfaces as in claim 1, wherein the insole is composed of a material having the selected coefficient of friction.
 4. The shoe for use on hard outdoor surfaces as in claim 1, wherein the front portion of the midsole is composed of ethylene vinyl acetate with a Shore A hardness of approximately
 35. 5. The shoe for use on hard outdoor surfaces as in claim 1, wherein the rear portion of the midsole is composed of ethylene vinyl acetate with a Shore A hardness of approximately
 45. 6. (canceled)
 7. A shoe for use on hard outdoor surfaces comprising an upper portion and a sole portion; said upper portion having, in the portion thereof covering the hindfoot, sufficient flexibility to deform in response to the upward ground-reaction force transmitted through the sole in the initial contact period of the walking gait cycle, and sufficient flexibility to deform in response to the motions of the hindfoot during hindfoot inversion; said sole portion being of substantially equal thickness throughout its length and lying substantially flat along its entire length when not subjected to bending forces, and comprising an insole portion, a midsole portion and an outsole portion; said insole portion having sufficient flexibility to bend at an angle of approximately 60° under the forces exerted by the foot from the heel rise to the toe-off periods of the walking gait cycle; said midsole portion comprising a front portion extending from the front of the shoe to a point between the ball of the foot and the front of the heel, and a rear portion extending from the back of the front portion to the back of the shoe; said front portion being composed of a material with sufficient flexibility to bend at an angle of approximately 60° under the forces exerted by the foot from the heel rise to the toe-off periods of the walking gait cycle, and with a level of resilience such as to provide shock absorption for the forefoot upon forefoot contact without springiness; said rear portion being composed of a material with a level of resilience such as to provide shock absorption for the heel of the foot upon heel strike without springiness; said outsole portion composed of a material with sufficient flexibility to bend at an angle of approximately 60° under the forces exerted by the foot from the heel rise to the toe-off periods of the walking gait cycle.
 8. The shoe for use on hard outdoor surfaces as in claim 7, wherein the front portion of the midsole is composed of ethylene vinyl acetate with a Shore A hardness of approximately
 35. 9. The shoe for use on hard outdoor surfaces as in claim 7, wherein the rear portion of the midsole is composed of ethylene vinyl acetate with a Shore A hardness of approximately
 45. 10. (canceled) 